1. Field of the Invention
The present invention concerns a contacting system and a method for contacting magnetic resonance local coils with a unit for additional signal processing of a magnetic resonance tomography apparatus, as well as a magnetic resonance tomograph with such a contacting system.
2. Description of the Prior Art
To examine a part of a human body it is known to introduce the body part to be examined into a homogenous magnetic field, known as the basic field. The magnetic field produces an alignment of the nuclear spins of atomic nuclei in the body part, in particular of atomic hydrogen nuclei (protons) bound to water. By means of radio-frequency excitation pulses, these nuclei are excited to a precession movement. After the end of an excitation pulse, the atomic nuclei precess with a frequency that depends on the strength of the basic field and then settle down again into the preferred direction predetermined by the basic field after a predetermined relaxation time due to their spins. The atomic nuclei thereby emit radio-frequency signals (known as magnetic resonance signals).
Through computational or measurement-related analysis of the integral magnetic resonance signals, an image can be generated from the spatial spin density or the distribution of the relaxation times within a body slice of an image. The association of the magnetic resonance signals (which can be tracked as a result of the precession movement) with the respective location of its generation ensues via application of linear field gradients. For this purpose, the corresponding gradient fields are superimposed on the basic field and controlled, and such that an excitation of the nuclei ensues only in a slice to be imaged. An image depiction based on these physical effects is known as “magnetic resonance tomography”.
For the most part, local surface coils (local coils)—also known as “loop antennas”—or array arrangements constructed from such loop antennas are used to acquire the magnetic resonance signals of an examination subject.
The magnetic resonance signals generated by the excited atomic nuclei induce a voltage in the reception antenna, which voltage is then amplified as an acquired magnetic resonance signal in a low-noise preamplifier, and are conducted via a cable to an additional amplifier device. The magnetic resonance signals—which are thus amplified twice—are then relayed via a further line to a unit for additional signal processing, via which unit they are processed further. Such a unit for additional signal processing is thus an electronic receiver unit that accepts the signals acquired by the local coils and prepares them—in particular amplifies and demodulates them—so that raw image data are created in a suitable form. Based on the raw data, volume image data and/or slice image data of an examination subject can then be reconstructed, normally with the assistance of additional processing units.
As mentioned, a preamplifier for amplification of the signals (that are then relayed via conductors and plugs with the additional processing unit) is conventionally located in every magnetic resonance local coil. Given a coverage of larger examination subjects from top to bottom with a plurality of magnetic resonance local coils, and/or given a use of multi-channel arrays, a correspondingly large number of conductors and plugs as well as units for additional signal processing or input channels into multi-channel units for additional signal processing are required. The number of units for additional signal processing or input channels in multi-channel units for additional signal processing is normally already limited for cost reasons.
Therefore, advantageously only those magnetic resonance local coils that are presently located in the acquisition field (field of view) of the magnetic resonance scanner are therefore connected to continuative electronic components. This creates the problem that the magnetic resonance local coils must each be coupled and decoupled again during the passage of an examination subject through the scanner.
Given such a passage, the movement of a subject positioning device therefore must be implemented discontinuously (for example clocked) in order to have the opportunity for recoupling. This significantly slows the examination workflow.